Refrigeration process and adsorbents therefor



Patented set. 13, 1934 1,947,381

REFRIGERATION ritocass Ann ADSORBENTS 'rnansroa' Gerald G. Connolly andErnest B. Miller, Baltimore, Md., assignor, by mesne assignments, toChester F. Hockley, receiver for The Silica Gel Corporation, Baltimore,MIL, a corporation of Maryland No Drawing. Application December 6, 1930Serial No. 500,668

:4 Claims. (Cl. 62-179) The present invention which is a continuationassociated therewith a substance capable of comin part of ourapplications Serial No. 427,649, blning readily with ammonia or an amineto filed February 11,1930 and Serial No. 470,227, form an ammino oramino compound respecfiled July 23, 1930, relates to refrigeration andtlvely, will adsorb ammonia or anamine in the 5 more particularly to thetype wherein the cooling gaseous state in an adsorption refrigerationsysefi ct is obtained by the evaporation of a liquid, tem without anysubstantial deterioration oi'the and the vapor is taken up in a solidporous ad; adsorbent material and without the formation of sorbent.permanentgases. I Refrigerating systems of this type may com- The solid,porous, adsorbent material may be 10 prise an evaporator or coolingchamber, contain= B d d-8 l containing at least One Oxide Such ing theliquid to be evaporated or fluid evapo- 'as the oxide of silicon,tungsten, tin, aluminum, ratedby expansion through an orifice, anadtitanium, a dried l containing WO sorber containing the adsorbingmaterial, and a e Of S d O d s e alumina-Silica a condenser forcondensing the vapor driven m material having a pore structure similarto that 15 from the adsorbing material and returning it to f a dr d s fxa pl as cha msaid evaporator or cooling chamber. Where solid pounds, oractivated carbon. The base excha e adsorbent material is employed fortaking upthe p s y be t natura Occurring 0mvapor from the coolingchamber, the adsorption p u ds such as auconite. suitablenaturalZoomustbe effected in the substantially totalabsence t a d the like. ore t fi a y p pa d 2c of permanent gases,or the rate of, adsorption willeflmpolmds. for instance. Sodium C omium 5111- be so reduced that aneirective cooling will not catc. potassium boron silicate. mvenadium besecured. One form of apparatus suitable for Silicate, and the liketheporous Structure the present invention is shown in Fig. 2 of Patem nBite! leaching the base h e 0 ent 1,729,031, granted September 24, 1929,pound with either acid or water. It is'to be 25 v ri u liquids maybeemployed in systems understood that any natural or artificial base thistype, for instance, sulphur dioxide, w t exchange compound may beemployed which has ammonia, oxides, activated charcoal, etc. Howa finepor S ru t materials m ever, not all of the adsorbents can be employed ted. a dried sels h as Silica gel is p f rr dwith anyone liquid, and,vice versa not all of The substances'with which the solid adsorbent sothe liquids can be employed with any one adsorbmater ay b impregnated ahose alts o ent. Many of the combinations of adsorbent and e p e ofreadily combining with am liquid will operate at first, but afterrepeated e an amine to form a metal ammino cycleseither ther is abreaking down .of' the amino compo d esp ctively, unde p essures vapor,gradually forming permanent gases, or h as Occur in refrigerating y m ofhe typ .35 else there is a reaction between the vapor and describedherein, and, when heated to drive 03 45 haps permanent gases are formed.

adsorbent that reduces the adsorptive power of liberate/the adsorbedammonia amine. W 9 i the adsorbing material. 7 v revert to the metalsalt and ammonia or amine Tests have shown that the combination ofsilica e p ct y- In ot w the Salts of gel as the adsorbent and ammoniaor an amine kmetals with which the adsorbent material is im- 40 as theliquid, after repeated activations, isnot .pregnated are those whichform simple or pri- 5 so satisfactory as the combination of sillcagelmary m ta amm n s r amines cf t rev rsible and sulphur dioxide, orsilica gel and water. It p Some Of t Salts the metals which yisthoughtthat with the ammonia or airline-silica ,be usedare lithiumchloride;.--silver nitrate or gel s stem, action on the gel injures it,and perhl id copp r sulp at ma n sium chlorideor sulphate; bariumchloride; calcium chloride; zinc" The principal feature of the presentinvention i d de, b o 'ehlolide, thiosultphate, P I is the provision ofan adsorption-refrigeration rate, chlorat ph s nitrate, ri or systemthat operates successfully with a solid, oxalate; strontium chloride;cadmium chloride or porous adsorbent and ammonia or an amine. sulphate;lead chloride; m anganous sulphate;

50 Another feature of the invention is that the and ferrous chloride orsulphate. Of the salts preferred adsorbent has a. veryigreatlyincreasedmentioned it is preferred to use those of the i effectivevadsorption capacity as compared with alkali forming metals such aslithium, calcium, or prior systems. i a j strontium chloride, althoughit is to be under- I It has also been found that a solid microporousstood that any of the other metal salts may 88 adsofiaent material,impregnated with or having also be used. no

Where it is desired to use an amine as the refrigerant, methylamine ispreferably employed. The amount of the metal salt with which theadsorbent material is impregnated is dependent 5 upon the particularmetal salt employed, and also the size of the pores of the adsorbentmaterial. When gaseous ammonia reacts or combines with the anhydrousmetal salt associated with the adsorbent material, the salt swells informing the metal ammino compound. The amount of swelling varies withthe diiferent metal salts and also the number of ammonia molecules withwhich the salt combines, for instance, 2, 4, 6, or more molecules. Uponrevivifying the adsorbent material, as by heating, the metal amminocompound is decomposed into the metal salt and ammonia, the ammoniabeing driven off and the metal salt remaining associated with theadsorbent material. An amine acts similarly in that it reacts orcombines with the anhydrous metal salt associated with the adsorbentmaterial to form a metal amino compound, and upon revivifying the adsorbent material, as by heating, the amino com-- -pound is decomposedinto the metal salt and amine, the amine being volatilized and drivenofi and the metal salt remaining. with the adsorbent material.

The pores of the adsorbent material should be only partially filled withthe metal salt, for, if completely filled, the swelling that resultsfrom the combination of the salt and ammonia or amine will rupture thewalls of the pores and thus injure or destroy the materials. adsorptioncapacity. It is a prerequisite that the pores of the adsorbent materialcontain only such an amount of the metal salt as will permit the ex-.

pansion of the metal ammino or amino compound without rupturing the porewalls. Samples of gel impregnated with 10% to 30% have given goodresults. The exact amount is dependent upon the salt and method ofimpregnation or the type of material impregnated.

As a specific example of the material that may be used in the invention,reference may be made to silica gel impregnated with lithium, strontium,or calcium chloride. This impregnated gel adsorbs ammonia or an amineboth chemically and physically, particularly when under pressures suchas occur in the refrigerating cycle described herein. The adsorbentmass, such as silica gel impregnated with about 30% or less of lithium,strontium, or calcium chloride, does not swell when adsorbing ammonia oran amine in the manner that usually occurs when lithium, strontium, orcalcium chloride by itself takes up ammonia or an amine. It has beendiscovered, according to the present invention, that there is a markedincrease in the adsorptive capacity of agel impregnated with calciumchloride, for ammonia or an amine, as compared with plain gel. Undernormal conditions occurring in the refrigerating cycle dc-,- scribedabove, that is, when the vapor is at about 20 F. and the condenser under120 pounds gauge pressure at F., plain silica gel adsorbs about 16%byjweight of ammonia, while silica gel impregnated' with 20% of calciumchloride adsorbs about 28%. After activation at 425 F., as usuallyoccurs in this cycle, the residual amount of ammonia or amine in theplain gel is about 6% and in the impregnated gel about 8%. Thus, for theplain silica gel the useful, saturation is about 10%, while for theimpregnated gel the useful saturation is about 20%. It has been foundthat the system calcium chloride impreg nated gel-ammonia or aminegivesabout twice the refrigeration that is secured with the system plaingel-sulphur dioxide.

The refrigerating adsorbent consisting of a solid, porous, adsorbentmaterial impregnated with a salt of a metal capable of combining withammonia or an amine to form a metal ammino or amino compound maybeprepared in any suitable manner. For example, a solid, porous, adsorbentmaterial, such as a gel, base exchange compound, or activated carbon, isimpregnated with a salt of a metal capable of combining with ammonia oran amine to form a metal ammino oramino compound. For this purpose anyone of the metal salts previously mentioned may be used.

One method is illustrated by the impregnation of an adsorbent materialwith a salt like lithium, strontium, or calcium chloride. The adsorbentmaterial is immersed or soaked in a 20% solution of either lithium,strontium, or calcium chloride for about 5 hours and then drained anddried. Before immersion in the salt solution, the adsorbent may betreated to prevent decrepitation, if desirable. The time ofsoakingshould be such that the pores are only partially filled with the salt,after the drying step.

Although the usual adsorbent materials, such asgels, base exchangecompounds, or activated carbons, may be employed, it is preferred to useadsorbents having larger pores than usually em-- ployed for gasadsorption, what may be termed wide pore adsorbents. As previouslyexplained, the pores should be only partially filled with the salt. Ifthe adsorbent employed has wide pores, then it can be charged orimpregnated with a larger percent by weight of the salt. Of course, thepores must not be enlarged to such an extent as to destroy or greatlyreduce their action as capillaries. An illustration is found in a gellike silica gel having wide pores impregnated with lithium chloride. Theapparent density of thematerial is an indication as to whether or not ithas large or small pores; Apparent density is theweight in grams of acubic centimeter of the material composed of particles having a definitesize, 1. e., particles that will pass an 8 mesh screen but remain on a20-=mesh screen. Silica gel having an apparent density of 0.65 or 0.7after activation at 600 F. has smaller pores than silica gel of a lessapparent ensity, say 0.6, after activation at 600 F. Th e are'variousmethods of preparing low density gels. According to one method,a-suitable washed hydrogel is impregnated with a substance soluble in aleaching medium chemically inert with respect to the gel, such .ascopper sulphate, aluminum chloride, sodium sulphate, calcium chloride,and the like, drying the impregnated hydrogel, and leaching out thesubstance with either water or acid, depending upon the particularsubstance used.

In this method a hydrogel is prepared in any suitable manner, forinstance, in accordance with the instructions given in the PatrickPatent No. 1,297,724, as by adding, with agitation, a solution of sodiumsilicate to an equal volume of an acid solution, such as a 10% solutionby weight of hydrochloric acid. the specific gravity of the silicatesolution being about 1.185. The ratio of SiOz to NaaO- in the silicatesolution may be as in ,any conunercial solution, about 3.25 to 1.

will

acid, and then soaked in a 10% to %.solution of the salt, say calciumchloride. for about 4' hours, although solutions of other strengths maybe employed. The solution is drained from the hydrogel, and then thehydrogel is dried in a current of air at about 125 C., which after atime I may be increased to 400 C.

This method of making. low density gels is claimed in application SerialNo. 444,880, filed 'April 16, 1930.

The salt impregnated gel is leached with water,

preferably hot water at about 180 F., and the shattering of the gelgranules.

leaching continued until substantially all of the :calcium chloride hasbeen removed or until the leaching water shows only a trace, when testedwith a solution of silver nitrate; Most of the calcium chloride leachesoutrather readily, and the resulting solution can be used again forimpregnating more 'hydrogel.

sired, the gel particles may be arranged in a thin layer and thenexposed to the atmosphere of the room in which steam introduced.

The strength of the calcium chloride or other may or may not beimpregnating solution may be varied according to convenience, and thetemperature at which the soluble material is leached out likewise may bevaried according to convenience or necessity.

Here it is preferable, but not essential, to re- I activate the leachedgel at a relatively high temperature, say 1000 F. p

The next step consists in charging the enlarged or wide pore gel withthe desired salt such as lithium or arontium chloride. For this purposethe gel is immersed in the salt solution, say a 10% to 15% solution, fora time sufficient to only partially flll the pores. If the gel is o1 atype that decrepitates, it may be partly charged with water vapor, aspreviously described, beforeimmersing in the salt solution. As the sizeof the pores in difierent adsorbents varies, no rule applicable to alladsorbents can be given as 'tothe length of time for this treatment. Fora gel made by the foregoing process, the immersion in the salt solutionshould last for about one hour or more, or

the salt solution of proper strength may be sprayed on the r gel.Usually the necessary amount of the salt solution, say 20% of the weightof the dry gel, is sufficient so that the solution will be just adsorbedby the pore space.

ZIhen the solution is drained from the gel, and it is dried or activatedas by passing a current of air at 600 F. over the same for about 3hours.

According to another method of accomplishing this final step, the lowdensity driedgel is impregnated with, say 30% or 40% of the dry weightof the gel with the salt, and this is immersed in water for a short timeto reduce the salt content to the desired amount, say 20%.

It is to be understood that the process just described gives a verysatisfactory product, .but the invention is not limited to a productmade in this way, as any other satisfactory process might be employed.

As an example of a method of making a salt impregnated alumina-silicagel, the following may be given. An alumina jelly is prepared by mixingequal volumes of a solution of aluminum sulphate of about 5% to 10%strength and a normal alkali solution such-as sodium'hydroxide orammonium The intermixed mass of alumina-silicajelly and hydrogel issoaked in a solution of the salt,-

say lithium, strontium, or calcium chloride of about 10% to 15% strengthfor about 4 hours. Thereafter the solution is drained from the jelly,and the jelly is dried in a current of air at 125 0., which aftersometime may be increased to 400 C.

Although the impregnated adsorbent materials have been described inconnection with refrigeration processes, they may also be used inprocesses for recovering ammonia or amines from gas mixtures containingthese compounds. Such process comprises adsorbing I the ammonia or aminecontained in the gas mixture :in a solid porous adsorbent materialimpregnated with a metal salt capable of combining with ammonia or amineto form metal amminoor amino compounds respectively, with or withoutpressure, and then recovering the adsorbed ammonia or amine as byheating the adsorbent material.

The term evaporating as used herein is intended to apply to any meansfor causing vapor to form from a liquid, whether by'heat, or ex-'pansion through an orifice, or otherwise.

In the claims, the term amo is used to designate both ammonia and anamine; the term amocompound to cover the compounds obtained when asubstance capable of combining with ammonia or an amine is contactedwith ammonia or an amine to form an ammino or amino compound; and theterm metal :amo compound to cover both the metal ammino and amino.compounds formed when a metal salt combines with ammonia or an-aminerespectively.

Having thus described the invention, what is .claimed as new and desiredto be secured-by Letters Patent is: I

1. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gaseous amo, in the substantial absence ofpermanent-gases, in a sorbent consisting of a gel in pregnated' with asubstance capable of com bining with said amo to form an amo compound.

2. The method according to claim 1 wherein the sorbent is silica gel.

3. The, method of refrigeration consistingin ice evaporating liquid amoand adsorbing the gaseous ,amo, in the substantial absence of permanentgases, in a sorbent consisting of a gel impregnated with a salt of ametal capable of combining with said amo to form a metal amo compound.

4. The method according to claim 3 in the gel is silica gel.

5. The method according to claim 3 wherein the gel is silica-aluminagel.

6. The method according to claim 3 wherein the metal salt is calciumchloride.

where- 7. The method according to claim 3 wherein the metal salt islithium chloride.

8. The method according to claim 3 wherein the metal salt is strontiumchloride.

9. The method according to claim 3 wherein the sorbent is only partiallycharged with the salt.

10. The method of refrigeration consisting in evaporating liquid amo andadsorbing the gaseous amo, in the substantial absence of permanentgases, in a sorbent consisting of silica gel impregnated with a salt ofa metal capable of combining with said amo to form a metal amo compound,and activated to a water content of less than 4%. 1

11. The method according to claim 10 wherein the salt is calciumchloride.

12. The method according to claim 10 wherein the salt is lithiumchloride.

13. The method according to claim 10 wherein the salt is strontiumchloride.

14. The method according to claim 10 wherein the gel is silica-aluminagel.

15. The method according to claim 10 wherein the sorbent is onlypartially charged with the salt.

16. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gas- 18. A method of refrigeration consisting inevaporating liquid amo and adsorbing the gaseous amo, in the substantialabsence of perma nent gases, in a sorbent consisting of aluminasilicagel impregnated with strontium chloride, the amount of the alumina beingnot substantially greater than 10% of the weight of the silica.

19. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gaseous amo, in the substantial absence of permanentgases, in a sorbent consisting of aluminasilica impregnated with calciumchloride.

20. A method-of refrigeration consisting in evaporating liquid amo andadsorbing the gaseous amo, in the substantial absence of permanentgases, in a sorbent consisting of aluminasilica impregnated with lithiumchloride.

21. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gaseous amo, in the substantial absence of perma nentgases, in a sorbent consisting of aluminasilica impregnated withstrontium chloride.

22. A method of refrigeration consisting in evaporating liquid amo and.adsorbing the gas- 100 eous amo, in the substantial absence of permanentgases, in a sorbent consisting of silica gel impregnated with calciumchloride.

23. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gas- 105 eous amo, in the substantial absence of permanentgases, in a sorbent consisting of silica gel impregnated with lithiumchloride.

24. A method of refrigeration consisting in evaporating liquid amo andadsorbing the gas- 110 eous amo, in the substantial absence of permanentgases, in a sorbent consisting of silica gel impregnated with strontiumchloride.

GERALD C. CONNOLLY. ERNEST B. MILLER.

